In the state of the art, use has already been proposed of the technique of 3D wavelet picture decomposition in which a group of pictures or GOP is decomposed according to a process which applies a wavelet decomposition to a two-dimensional or 2D picture. On this basis, one then performs a compression of the data stream along the time dimension which plays the role of a third dimension.
In the state of the art, the trickiest point occurs during the wavelet temporal decomposition. When the temporal decomposition has been performed, the pixels that are joined by a motion vector in the GOP picture sequence have been tagged. Now, it is appreciated that pixels through which no motion vector passes are missing when we perform the compression operation along the time dimension.
To solve this problem and avoid losing information during processing, it is therefore necessary to apply a particular processing to these pixels, thereby reducing the efficiency of the wavelet processing.
In the usual video coding schemes, the motion is described by blocks, 16 pixels wide by 16 pixels high, for example. The problem raised above is then shifted to the boundaries of the blocks.
To solve this problem, account has also been taken of the trajectories of the pixels in the two running directions of the picture sequence: in the natural direction of the GOP picture sequence and in the opposite direction. However, one then doubles the quantity of motion information with respect to the conventional techniques.
To afford a remedy to these drawbacks of the state of the art, the present invention consists in choosing configuration data for each sequence and an optimizing criterion making it possible to reduce the number of unconnected pixels in each GOP picture sequence.
It follows that the number of unconnected pixels is considerably reduced without requiring more processing according to a 3D wavelet decomposition.